U.S. patent application number 10/230259 was filed with the patent office on 2003-06-26 for apparatus for inspecting a heat exchanger tube and group of heat exchanger tubes.
Invention is credited to Ara, Kuniaki, Hayashida, Hitoshi, Hirabayashi, Masaru.
Application Number | 20030118150 10/230259 |
Document ID | / |
Family ID | 19188765 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030118150 |
Kind Code |
A1 |
Hirabayashi, Masaru ; et
al. |
June 26, 2003 |
Apparatus for inspecting a heat exchanger tube and group of heat
exchanger tubes
Abstract
An apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in which a
multiplicity of heat exchanger tubes are arranged. The apparatus
comprises a radiation detector 12 inserted in a heat exchanger tube
10a to be inspected, at least one radiation source 14 inserted in a
plurality of heat exchanger tubes surrounding the heat exchanger
tube 10a to be inspected, and a CT processing unit 16 for
subjecting radiation strength signals detected by the radiation
detector 12 to a CT processing. A cross section of the heat
exchanger tube 10a to be inspected is imaged by the CT processing.
By setting at least one radiation source 56 in an inner portion of
the heat exchanger tube, on the inner side of a group 50 of heat
exchanger tubes or on the outer side of the group 50 of heat
exchanger tubes, and by setting at least one radiation detector 58
carrying a collimator 60 on the outer side of the group 50 of heat
exchanger tubes so that radiations emitted from the radiation
source 56 can be detected over substantially the whole
circumference of the group 50 of heat exchanger tubes, a cross
section of the group 50 of heat exchanger tubes can be imaged by
the CT processing.
Inventors: |
Hirabayashi, Masaru;
(Higashi-Ibaraki-gun, JP) ; Ara, Kuniaki;
(Higashi-Ibaraki-gun, JP) ; Hayashida, Hitoshi;
(Higashi-Ibaraki-gun, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
19188765 |
Appl. No.: |
10/230259 |
Filed: |
August 29, 2002 |
Current U.S.
Class: |
378/59 |
Current CPC
Class: |
F28F 2265/16 20130101;
F22B 37/003 20130101 |
Class at
Publication: |
378/59 |
International
Class: |
G01B 015/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2001 |
JP |
2001-393383 |
Claims
What is claimed is:
1. An apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in which a
multiplicity of heat exchanger tubes are arranged, the apparatus
comprising: a radiation detector inserted in a heat exchanger tube
to be inspected, at least one radiation source inserted in a
plurality of heat exchanger tubes surrounding the heat exchanger
tube to be inspected, and a CT processing unit for subjecting
radiation strength signals detected by the radiation detector to a
CT processing, whereby a cross section of the heat exchanger tube
to be inspected is imaged by the CT processing.
2. An apparatus for inspecting a heat exchanger tube according to
claim 1, wherein a plurality of radiation sources are inserted in
the plurality of heat exchanger tubes adjoining substantially the
whole circumference of the heat exchanger tube to be inspected
having the radiation detector inserted therein, whereby a cross
section of the heat exchanger tube having the radiation detector
inserted therein is imaged by the CT processing.
3. An apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in which a
multiplicity of heat exchanger tubes are arranged, the apparatus
comprising: a radiation detector inserted in a heat exchanger tube
to be inspected, at least one radiation source set in the interior
of a plurality of heat exchanger tubes and additionally disposed
simulated heat exchanger tubes surrounding the heat exchanger tube
to be inspected, and a CT processing unit for subjecting radiation
strength signals detected by the radiation detector to a CT
processing, whereby a cross section of the heat exchanger tube to
be inspected is imaged by the CT processing.
4. An apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in a nuclear
reactor plant in which a multiplicity of heat exchanger tubes are
arranged, the apparatus comprising: a radiation detector inserted
in a heat exchanger tube to be inspected and a CT processing unit
for subjecting radiation strength signals detected by the radiation
detector to a CT processing, whereby radiations emitted from
radioactive nuclides produced in a nuclear reactor coolant are
detected by the radiation detector, and a cross section of the heat
exchanger tube to be inspected is imaged by the CT processing.
5. An apparatus for non-destructively inspecting a group of heat
exchanger tubes in which a multiplicity of heat exchanger tubes are
arranged, the apparatus comprising: at least one radiation source
set in at least one of the positions selected from a position in an
inner portion of the heat exchanger tube, a position on the inner
side of the group of heat exchanger tubes or a position on the
outer side of the group of heat exchanger tubes, at least one
radiation detector carrying a collimator set in a position on the
outer side of the group of heat exchanger tubes so that radiations
emitted from the radiation source can be detected by the
collimator-carrying radiation detector over substantially the whole
circumference of the group of heat exchanger tubes, and a CT
processing unit for subjecting radiation strength signals detected
by the collimator-carrying radiation detector to a CT processing,
whereby a cross section of the group of heat exchanger tubes is
imaged by the CT processing.
6. An apparatus for non-destructively inspecting a group of heat
exchanger tubes in a nuclear reactor plant in which a multiplicity
of heat exchanger tubes are arranged, the apparatus comprising: at
least one radiation detector carrying a collimator set in a
position on the outer side of the group of heat exchanger tubes so
that radiations can be detected by the collimator-carrying
radiation detector over substantially the whole circumference of
the group of heat exchanger tubes, and a CT processing unit for
subjecting radiation strength signals detected by the
collimator-carrying radiation detector to a CT processing, whereby
radiations emitted from radioactive nuclides produced in a nuclear
reactor coolant are detected by the collimator-carrying radiation
detector, and a cross section of the group of heat exchanger tubes
is imaged by the CT processing.
7. An apparatus for inspecting a group of heat exchanger tubes
according to claim 5 or 6, wherein a plurality of
collimator-carrying radiation detectors are set on the outer side
of the group of heat exchanger tubes at substantially uniform
intervals over substantially the whole circumference of the group
of heat exchanger tubes.
8. An apparatus for inspecting a group of heat exchanger tubes
according to claim 5 or 6, wherein a single or a plurality of
collimator-carrying radiation detectors are set on the outer side
of the group of heat exchanger tubes so that the
collimator-carrying radiation detector can be moved in the
circumferential direction of the group of heat exchanger tubes.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus for
non-destructively inspecting a heat exchanger tube and a group of
heat exchanger tubes, and more particularly to an apparatus for
inspecting a heat exchanger tube or a group of heat exchanger tubes
for a defect by imaging a cross section thereof by CT (Computed
Tomography) processing by utilizing radiations. This technique is
suitably applied to the diagnosing of a defect of a heat exchanger
tube used in, for example, a heat exchanger, a steam generator, a
boiler and the like.
[0002] A heat exchanger and a steam generator and the like
generally have a structure in which a group of heat exchanger tubes
constructed by arranging and bundling a multiplicity of heat
exchanger tubes are incorporated in a container. The use of these
heat exchanger tubes under severe conditions for a long period of
time gives rise to a fear of the occurrence of various kinds of
defects therein. Therefore, it is necessary to carry out a
non-destructive inspection of heat exchanger tubes periodically, or
at any time as occasion demands.
[0003] Typical non-destructive inspection methods which have
heretofore been carried out in practice include a visual inspection
method, an ultrasonic wave inspection method, an eddy current
inspection method and the like. The visual inspection method is a
method of inserting an optical device, such as a reflecting mirror,
a camera and the like in the vicinity of an object to be inspected,
and observing the object directly or indirectly. The ultrasonic
wave inspection method is a method of conducting flaw detection,
thickness measurement and the like by sending an ultrasonic pulse
toward an object to be inspected, receiving a reflected wave from
an interface, etc. of the object, converting the received wave into
an electric signal, and continuing observation of the electric
signal for a given length of time. The eddy current inspection
method is a method of determining the existence or non-existence of
a defect and measuring the thickness of an object by supplying an
AC current to a test coil, and detecting an eddy current induced by
the object to be inspected, with reference to the variation of
impedance of the coil. These non-destructive inspection methods are
usually carried out from the inner side of a heat exchanger tube
for the reason that the accessing to the object to be inspected is
done easily.
[0004] However, these inspection methods have various problems that
only an inner surface of the heat exchanger tube can be inspected,
that a double tube or a triple tube having a clearance between an
outer tube member and an inner tube member cannot be inspected,
that a tube made of a magnetic material are difficult to be
inspected, and the like. Therefore, these inspection methods have
to be selectively used in accordance with the material,
construction and a portion to be inspected of the heat exchanger
tube. As a result, an inspecting operation cannot be carried out
fully satisfactorily in some cases, and an inspecting operation
becomes complicated in other cases.
[0005] Further, these prior art inspection methods are directed to
a single heat exchanger tube only, and incapable of observing the
whole of a group of heat exchanger tubes and diagnosing various
kinds of defects thereof.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide an
apparatus capable of non-destructively and easily inspecting a heat
exchanger tube and a group of heat exchanger tubes for a defect, a
wall thickness and the like regardless of the material and
construction of the heat exchanger tube or of the condition of
arrangement of a multiplicity of heat exchanger tubes.
[0007] According to the present invention, there is provided an
apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in which a
multiplicity of heat exchanger tubes are arranged, the apparatus
comprising: a radiation detector inserted in a heat exchanger tube
to be inspected, at least one radiation source inserted in a
plurality of heat exchanger tubes surrounding the heat exchanger
tube to be inspected, and a CT processing unit for subjecting
radiation strength signals detected by the radiation detector to a
CT processing, whereby a cross section of the heat exchanger tube
to be inspected is imaged by the CT processing.
[0008] As heat exchanger tubes in which the radiation source is to
be inserted, it is most simple to select heat exchanger tubes
adjoining the heat exchanger tube to be inspected. However, as long
as the radiation detector in the heat exchanger tube to be
inspected can detect radiations transmitted through the heat
exchanger tubes, the radiation source may be inserted in a heat
exchanger tube disposed away from the heat exchanger tube to be
inspected with other heat exchanger tubes interposed
therebetween.
[0009] According to the present invention, there is also provided
an apparatus for non-destructively inspecting an arbitrary heat
exchanger tube among a group of heat exchanger tubes in which a
multiplicity of heat exchanger tubes are arranged, the apparatus
comprising: a radiation detector inserted in a heat exchanger tube
to be inspected, at least one radiation source set in the interior
of a plurality of heat exchanger tubes and additionally disposed
simulated heat exchanger tubes surrounding the heat exchanger tube
to be inspected, and a CT processing unit for subjecting radiation
strength signals detected by the radiation detector to a CT
processing, whereby a cross section of the heat exchanger tube to
be inspected is imaged by the CT processing.
[0010] The simulated heat exchanger tube may be, for example, a
tubular body having the same outer shape and formed of the same
material as the heat exchanger tube. The additional disposition of
the simulated heat exchanger tubes especially effective in the case
where the heat exchanger tube disposed on the circumferentially
outermost portion is inspected.
[0011] According to the present invention, there is further
provided an apparatus for non-destructively inspecting an arbitrary
heat exchanger tube among a group of heat exchanger tubes in a
nuclear reactor plant in which a multiplicity of heat exchanger
tubes are arranged, the apparatus comprising: a radiation detector
inserted in a heat exchanger tube to be inspected and a CT
processing unit for subjecting radiation strength signals detected
by the radiation detector to a CT processing, whereby radiations
emitted from radioactive nuclides produced in a nuclear reactor
coolant are detected by the radiation detector, and a cross section
of the heat exchanger tube to be inspected is imaged by the CT
processing.
[0012] When a group of heat exchanger tubes (for example, a heat
exchanger, a steam generator and the like) are incorporated in a
nuclear reactor plant, it is possible to directly utilize
radiations emitted from radioactive nuclides (for example,
sodium-22, sodium-24 and the like) in a coolant as a radiation
source. These radioactive nuclides in the coolant are produced by
nuclear reactions of coolant sodium and neutrons in the nuclear
reactor.
[0013] According to the present invention, there is also provided
an apparatus for non-destructively inspecting a group of heat
exchanger tubes in which a multiplicity of heat exchanger tubes are
arranged, the apparatus comprising: at least one radiation source
set in at least one of the positions selected from a position in an
inner portion of the heat exchanger tube, a position on the inner
side of the group of heat exchanger tubes or a position on the
outer side of the group of heat exchanger tubes, at least one
radiation detector carrying a collimator set in a position on the
outer side of the group of heat exchanger tubes so that radiations
emitted from the radiation source can be detected by the
collimator-carrying radiation detector over substantially the whole
circumference of the group of heat exchanger tubes, and a CT
processing unit for subjecting radiation strength signals detected
by the collimator-carrying radiation detector to a CT processing,
whereby a cross section of the group of heat exchanger tubes is
imaged by the CT processing.
[0014] According to the present invention, there is further
provided an apparatus for non-destructively inspecting a group of
heat exchanger tubes in a nuclear reactor plant in which a
multiplicity of heat exchanger tubes are arranged, the apparatus
comprising: at least one radiation detector carrying a collimator
set in a position on the outer side of the group of heat exchanger
tubes so that radiations can be detected by the collimator-carrying
radiation detector over substantially the whole circumference of
the group of heat exchanger tubes, and a CT processing unit for
subjecting radiation strength signals detected by the
collimator-carrying radiation detector to a CT processing, whereby
radiations emitted from radioactive nuclides produced in a nuclear
reactor coolant are detected by the collimator-carrying radiation
detector, and a cross section of the group of heat exchanger tubes
is imaged by the CT processing.
[0015] A multiplicity of collimator-carrying radiation detectors
may be set on the outer side of the group of heat exchanger tubes
at substantially uniform intervals over substantially the whole
circumference of the group of heat exchanger tubes. Alternatively,
a single or a plurality of collimator-carrying radiation detectors
may be set on the outer side of the group of heat exchanger tubes
so that the collimator-carrying radiation detector can be moved in
the circumferential direction of the group of heat exchanger tubes.
In either case, transmission strength data of radiations can be
obtained over the whole circumference of the group of heat
exchanger tubes.
[0016] The "CT" generally means a method of obtaining a
cross-sectional image of an object to be inspected by calculation
based on measured values of projection amounts in various
directions by utilizing X-rays, ultrasonic waves, various kinds of
corpuscular rays and the like. In the present invention, radiations
(X-rays or .gamma.-rays) are utilized. The radiations sent out from
radiation sources placed in various positions transmit an object to
be inspected, and the transmitted radiations are detected by the
radiation detector. Signals obtained by detecting the transmitted
radiations are subjected to calculation in a computer, and the
object to be inspected is thereby restructured as a cross-sectional
image, which is then displayed.
[0017] In the present invention, when a driving mechanism capable
of moving one or both of the radiation source and the radiation
detector in the axial direction of the heat exchanger tube is
provided, inspecting the heat exchanger tube in the axial direction
thereof becomes possible. In the case of the group of heat
exchanger tubes incorporated in the nuclear reactor plant, by
providing a driving mechanism capable of moving the radiation
detector in the axial direction of the heat exchanger tube, the
inspection of the heat exchanger tube in the axial direction
thereof becomes possible. As a result, it is possible to obtain
cross-sectional images of the whole length of the heat exchanger
tube or the group of heat exchanger tubes, continuously throughout
the length thereof or intermittently at desired intervals of the
length thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A, 1B are explanatory drawings showing an embodiment
of the apparatus for inspecting heat exchanger tubes according to
the present invention.
[0019] FIGS. 2A, 2B are drawings illustrating a CT processing
operation.
[0020] FIG. 3 is an explanatory drawing showing another embodiment
of the apparatus for inspecting heat exchanger tubes according to
the present invention.
[0021] FIG. 4 is an explanatory drawing showing an example in which
the present invention is applied to the inspection of a multiplex
heat exchanger tube.
[0022] FIG. 5 is an explanatory drawing showing still another
embodiment of the apparatus for inspecting heat exchanger tubes
according to the present invention.
[0023] FIG. 6 is an explanatory drawing showing a further
embodiment of the apparatus for inspecting heat exchanger tubes
according to the present invention.
[0024] FIGS. 7A, 7B are explanatory drawings showing an embodiment
of the apparatus for inspecting a group of heat exchanger tubes
according to the present invention.
[0025] FIG. 8 is an explanatory drawing showing another embodiment
of the apparatus for inspecting a group of heat exchanger tubes
according to the present invention.
[0026] FIG. 9 is an explanatory drawing showing an example in which
the present invention is applied to the inspection of a multiplex
tube.
PREFERRED EMBODIMENTS OF THE INVENTION
[0027] FIGS. 1A and 1B are an explanatory drawings showing an
embodiment of the apparatus for inspecting heat exchanger tubes
according to the present invention, wherein FIG. 1A is a horizontal
sectional view of the heat exchanger tubes; and FIG. 1B is a
longitudinal sectional view thereof. This apparatus is adapted to
non-destructively inspect an arbitrary heat exchanger tube by
utilizing radiations (X-rays or .gamma.-rays).
[0028] In the inside of a heat exchanger and a steam generator, a
multiplicity of heat exchanger tubes 10 are incorporated in a
regularly arranged state (which are called a group of heat
exchanger tubes). The present invention provide the apparatus for
inspecting a heat exchanger tube comprising a radiation detector 12
inserted in a heat exchanger tube to be inspected (a heat exchanger
tube drawn in the center of FIG. 1, and this tube is shown
specially by a reference numeral 10a), at least one radiation
source 14 inserted in a plurality of heat exchanger tubes adjacent
to and surrounding the heat exchanger tube 10a to be inspected, and
a CT processing unit 16 adapted to subject transmission strength
signals of the radiations, which are detected by the radiation
detector 12, to the CT processing. A cross section of the heat
exchanger tube 10a is imaged by this CT processing unit 16 in an
arbitrary position in the axial direction of the heat exchanger
tube 10a.
[0029] An outline of the CT processing is as follows. As shown in
FIG. 2A, a radiation sent out from a radiation source 32 is applied
to an object 30 to be inspected in one direction. The
transmissivity (or absorptivity) of the radiation which has
transmitted through the object 30 is detected by a radiation
detector. The transmissivity of the radiation becomes low in a
thick portion of the object 30 to be inspected, and high in a thin
portion thereof. As shown in FIG. 2B, when the transmissivity (or
absorptivity) of a radiation which is applied to the object 30 in
another direction is measured, the thickness, etc. of the object in
its direction can be detected. This operation is carried out over
the whole circumference of the object 30. When these data on the
transmissivity (or absorptivity) are synthesized, a cross-sectional
image of the object 30 in an arbitrary position can be obtained.
This is a general description of the CT (Computed Tomography)
method using radiations.
[0030] Returning to FIG. 1A, a heat exchanger tube 10a to be
inspected (heat exchanger tube in which a radiation detector 12 is
inserted) is adjoined and surrounded by eight heat exchanger tubes
10, and a radiation source 14 is inserted into the plurality of
heat exchanger tubes 10 one by one, in order. The radiation (shown
by an arrow r) sent out from the radiation source 14 transmits
through the heat exchanger tube 10 in which the radiation source 14
is inserted and the heat exchanger tube 10a in which the radiation
detector 12 is inserted, and detected by the radiation detector 12.
Since the radiation source 14 is inserted one by one, in order,
into the heat exchanger tubes 10 which surround substantially the
whole circumference of the heat exchanger tube 10a to be inspected,
the radiations transmitted through substantially the whole
circumference of the heat exchanger tube 10a can be detected by the
radiation detector 12. When transmission strength signals of all
the radiations thus detected are processed in a CT processing unit
16, a cross section of the heat exchanger tube 10a to be inspected
can be imaged in an arbitrary position in the axial direction
thereof. The heat exchanger tube 10a can be inspected for a defect,
etc. on the basis of the obtained image.
[0031] When the radiation detector 12 is then inserted into another
heat exchanger tube to be inspected and the radiation source 14 is
inserted one by one, in order, into the other heat exchanger tubes
surrounding the radiation detector-containing heat exchanger tube,
a cross section of the radiation detector-containing heat exchanger
tube can be imaged. By inserting the radiation detector 12 one by
one in order into all the heat exchanger tubes desiring to be
inspected and carrying out such an operation as described above,
cross sections of all the heat exchanger tubes desiring to be
inspected can be imaged, so that all the tubes can be inspected for
defects, etc. In the apparatus according to the present invention,
a plurality of radiation sources 14 may be inserted into the
respective heat exchanger tubes 10 adjoining and surrounding the
heat exchanger tube 10a to be inspected. In this case, the
radiation detector 12 inserted in the heat exchanger tube 10a
detects the radiations sent out from the radiation sources 14 one
by one, in order.
[0032] As shown in FIG. 1B, when the radiation detector 12 and the
radiation source 14 are moved synchronously to arbitrary vertical
positions by a vertically driving mechanism 36, the radiations
which have transmitted through the heat exchanger tubes can be
detected in these vertical positions. Accordingly, when an
operation for subjecting strength signals of the transmitted
radiations to the CT processing is carried out continuously or
intermittently at suitable intervals over the whole length of the
heat exchanger tubes, a cross section of the heat exchanger tubes
in the respective positions in the axial direction thereof can be
imaged. Such operations enable to obtain the images of the heat
exchanger tubes as a whole and to carry out the defect inspection
in the heat exchanger tubes utilizing the images thus obtained.
[0033] FIG. 3 shows an example in which the condition of
arrangement of the heat exchanger tubes is changed. The present
invention employs a system having the radiation detector 12
inserted in an inner portion of the heat exchanger tube 10a to be
inspected, and at least one radiation source 14 inserted into inner
portions of a plurality of other heat exchanger tubes 10
surrounding the tube 10a to be inspected. Therefore, no matter how
the condition of arrangement of the heat exchanger tubes is
changed, an operation for inspecting the heat exchanger tubes can
be carried out correspondingly without any trouble. Since the
present invention also employs a system for detecting transmitted
radiations, the invention can be applied to a group of heat
exchanger tubes each of which is made of a multiplex tube, such as
a double tube and a triple tube. FIG. 4 shows an example of a heat
exchanger tube 40 having a triple structure. As shown in FIG. 4,
the radiation detector 12 is inserted into the inside of an
innermost tube member. The present invention can also be applied to
a case where other structural members 42 (for example, support
members and the like for the heat exchanger tube) are disposed in a
clearance between tube members constituting the heat exchanger tube
40 of the triple structure or between adjacent heat exchanger
tubes.
[0034] The above embodiment describes a case where the radiation
source is inserted into the heat exchanger tubes adjacent to the
heat exchanger tube in which the radiation detector is inserted.
However, as long as the transmission strength data of the
radiations are obtained over the whole circumference of the heat
exchanger tube in which the radiation detector is inserted, the
heat exchanger tubes in which the radiation source 14 is inserted
may not necessarily be adjacent to the heat exchanger tube 12 in
which the radiation detector 12 is inserted, as shown in FIG.
5.
[0035] When the heat exchanger tubes are arranged in this manner,
it becomes possible to image the cross sections of the heat
exchanger tube in which the radiation detector 12 is inserted and
the surrounding heat exchanger tubes by CT processing, and inspect
a plurality of heat exchanger tubes at once. A reference numeral 18
denotes a cylindrical container in which a group of heat exchanger
tubes are housed.
[0036] FIG. 6 shows an example of a case where a circumferentially
outermost heat exchanger tube is inspected. When the
circumferentially outermost heat exchanger tube is inspected, the
radiation source can be inserted in a heat exchanger tube adjacent
to and on the inner side of the heat exchanger tube to be
inspected, but the radiation source cannot be inserted in a heat
exchanger tube on the outer side of the heat exchanger tube to be
inspected since a heat exchanger tube does not exist on the outer
side of the heat exchanger tube to be inspected. Therefore, when
the heat exchanger tubes are left as they are, the transmission
strength data of the radiation over the whole circumference of the
heat exchanger tube to be inspected cannot be obtained. Under the
circumstances, between a group of heat exchanger tubes consisting
of a multiplicity of heat exchanger tubes 10 and the cylindrical
container 18 surrounding these heat exchanger tubes 10, a
multiplicity of auxiliary simulated heat exchanger tubes 46, the
outer shape and material of which are the same as those of the
tubes 10, are disposed, and the radiation source 14a is inserted
into the inner portions of the simulated heat exchanger tubes 46.
The radiation source may, of course, be inserted directly in the
cylindrical container 18 without using the simulated heat exchanger
tubes 46. Since the constitution using the simulated heat exchanger
tubes 46 can always maintain the interior of the simulated heat
exchanger tubes in a liquid-less state, the constitution is
effective, especially when the cylindrical container 18 is filled
with a liquid. When there is not a sufficient space between the
group of heat exchanger tubes and the cylindrical container, the
radiation source may be disposed on the outer side of the
cylindrical container.
[0037] In the inspection of the heat exchanger tube carried out by
the apparatus according to the present invention, there may be used
a method of inserting the radiation source one by one into the heat
exchanger tubes around the radiation detector-containing heat
exchanger tube to be inspected, and detecting in order the
radiations sent out from the specific directions by the radiation
detector. Alternatively, there may be also used a method of
inserting the radiation source into one heat exchanger tube and
detecting the radiations at a plurality of positions on the whole
circumference of the radiation source-containing heat exchanger
tube by using a radiation detector carrying a collimator.
[0038] FIGS. 7A and 7B are explanatory drawings showing an
embodiment of the apparatus for inspecting a group of heat
exchanger tubes according to the present invention, wherein FIG. 7A
illustrates a horizontal section of a group of heat exchange tubes;
and FIG. 7B illustrates a longitudinal section thereof. This
apparatus is adapted to non-destructively inspect a group of heat
exchanger tubes as a unit by utilizing radiations (X-rays or
.gamma.-rays).
[0039] The group 50 of heat exchanger tubes has a structure in
which a multiplicity of vertically extending heat exchanger tubes
52 are arranged regularly and bundled with a suitable distance kept
from one another, and these heat exchanger tubes 52 are
incorporated in a cylindrical container 54. The radiation source 56
can be set in an inner portion of an arbitrary heat exchanger tube
(for example, a position designated by a reference letter a), in an
arbitrary position on the inner side of the group of heat exchanger
tubes (for example, a position designated by a reference letter b),
or in an arbitrary position on the outer side of the group of heat
exchanger tubes (for example, a position designated by a reference
letter c). When measurement is conducted in practice, the radiation
source 56 is inserted into one of the positions of the interior of
the heat exchanger tube, the inside of the group of heat exchanger
tubes or the outside of the same group in accordance with the
actual condition, and not into all of these positions at the same
time. FIGS. 7A and 7B show an example in which the radiation source
56 is inserted into the interior of the central heat exchanger tube
as shown by a solid line.
[0040] On the outer side of the cylindrical container 54, namely on
the outer side of the group of heat exchanger tubes, a radiation
detector 58 is set so that the radiations can be detected in an
arbitrary position over substantially the whole circumference of
the cylindrical container 54. This radiation detector 58 is formed
so that a detecting surface thereof faces to the group of heat
exchanger tubes with a cylindrical collimator 60 attached to the
front side of the detecting surface thereof. Owing to the
collimator-carrying radiation detector 58 described above, only the
radiations that enter the collimator 60 along the axis thereof are
selectively detected. A radiation strength signals detected by the
radiation detector 58 is sent to a CT processing unit 62 and
subjected to the CT processing, to thereby image a cross section of
the group of heat exchanger tubes at an arbitrary position.
[0041] The radiations sent out from the radiation source 56
transmit through the group 50 of heat exchanger tubes consisting of
a multiplicity of heat exchanger tubes 52, and through the
cylindrical container 54 surrounding the group of tubes. In the
radiation detector 58, only the transmitted radiations that have
passed through the collimator 60 in a predetermined direction are
detected. A multiplicity of collimator-carrying radiation detectors
58 may be arranged in a substantially uniformly distributed state
around the whole circumference of the cylindrical container 54, or
a single or a plurality of collimator-carrying radiation detectors
may be moved properly over the whole circumference of the
cylindrical container 58. Thus, the radiations transmitted through
the group of heat exchanger tubes in various directions with
respect thereto are detected by the collimator-carrying radiation
detector or detectors 58.
[0042] The position of each heat exchanger tube 52 is already
known, and those of the radiation source 56 and radiation detector
58 can be determined, so that the path along which the radiations
detected by the radiation detector 58 is known. Owing to the use of
the multiple distributed radiation detectors or the movement of a
single radiation detector, a multiplicity of signals of radiations
transmitted through the group 50 of the heat exchanger tubes to be
inspected are obtained. The detected signals are line integrals of
attenuation with respect to the radiations transmitted through a
propagation path. Therefore, when the signals in all directions
which are detected by the radiation detector 58 are subjected to
the CT processing, a horizontal section of the group of heat
exchanger tubes can be imaged. This image enables the inspection of
the heat exchanger tubes for a defect to be carried out.
[0043] As shown in FIG. 7B, when the radiation source 56 and the
radiation detector 58 are moved to arbitrary vertical positions by
a vertically driving mechanism 70, strength signals of the
radiations transmitted through the heat exchanger tubes in these
vertical positions can be detected. By carrying out an operation
for subjecting the signal to the CT processing at suitable
intervals along the vertical length of the group of heat exchanger
tubes, a cross section of the group of heat exchanger tubes at the
respective positions in the axial direction of the heat exchange
tubes can be imaged. Thus, it becomes possible to image the group
of heat exchanger tubes as a whole, and carry out the defect
inspection of the heat exchanger tubes by utilizing these
images.
[0044] Although the radiation detector 58 is disposed on the outer
side of the cylindrical container 54 surrounding the group of heat
exchanger tubes 52 in the above-described embodiment, such a
radiation detector may also be disposed in a space between the
group of heat exchanger tubes and the cylindrical container under a
certain condition. An example of such a case is shown in FIG. 8. In
this case, auxiliary measuring tubes 74 the shape of which is
identical with that of the heat exchanger tubes 52 are inserted in
a space between the group 50 of heat exchanger tubes consisting of
a multiplicity of heat exchanger tubes 52 and the cylindrical
container 54, and the radiation source 56a or the radiation
detector 58a may be inserted in the interior of the measuring tube
74. Alternatively, the radiation source 56b and the radiation
detector 58b may be inserted directly in the space without using
the measuring tubes. In the constitution using the measuring tubes
74, the interior of the measuring tubes 74 can always be maintained
in a liquid-less condition, so that this constitution is
effectively used, especially in a case where the interior of the
cylindrical container 54 is filled with a liquid.
[0045] The present invention is directed to a system for detecting
radiations which have transmitted through a heat exchanger tube,
and can therefore be applied to an inspection of a group of heat
exchanger tubes each of which is formed of a multiplex tube, such
as a double tube and a triple tube. FIG. 9 shows an example of a
heat exchanger tube 80 which has a triple structure. A radiation
source 82 is inserted in the interior of an innermost tube member
of the tube 80, or on the outer side of an outermost tube member.
The present invention can also be applied to even a case where
other structural members 84 (for example, support members for the
heat exchanger tubes) are disposed in a clearance between tube
members constituting the heat exchanger tube of the triple
structure, or between adjacent heat exchanger tubes.
[0046] In the apparatus according to the present invention, no
problem arises basically even when the radiation source is set only
in the interior of the heat exchanger tube, only on the inner side
of the group of heat exchanger tubes, or only on the outer side of
the group of heat exchanger tubes. However, in the following
condition, the position in which the radiation source is set poses
problems in some cases, so that it is necessary to designate the
position in which the radiation source is set.
[0047] (1) When the cylindrical container surrounding heat
exchanger tubes or a group of heat exchanger tubes is filled with a
liquid, for example, during an operation of a plant, it is
necessary to set the radiation source on the outer side of the
group of heat exchanger tubes.
[0048] (2) When the interior of the heat exchanger tube is filled
with a liquid but the interior of the cylindrical container is not,
the radiation source may be set either on the inner side of the
group of heat exchanger tubes or on the outer side thereof.
[0049] (3) When the interior of the cylindrical container is filled
with a liquid but the interior of the heat exchanger tube is not,
the radiation source may be set either in the heat exchanger tube
or on the outer side of the group of heat exchanger tubes.
[0050] (4) When neither the interior of the heat exchanger tube nor
that of the cylindrical container is filled with a liquid, the
radiation source may be set in any position.
[0051] In order to practically use the apparatus according to the
present invention, a radiation source is set on the outer side of
the group of heat exchanger tubes first, and the group of heat
exchanger tubes as a whole is then imaged. Then attention is paid
to a heat exchanger tube which is likely to have a defect. In order
to observe this heat exchanger tube more thoroughly, a liquid is
discharged, a radiation source is inserted on the inner side of the
group of heat exchanger tubes, and the inspection of the heat
exchanger tubes is then conducted. In order to obtain a cross
sectional image of the group of heat exchanger tubes by carrying
out a CT processing operation, it is necessary to obtain
transmission strength data of the radiations (X-rays or
.gamma.-rays) over the whole circumference of the group of heat
exchanger tubes. Therefore, when the radiation source is inserted
in any position of the interior of the heat exchanger tube, on the
inner side of the group of heat exchanger tubes or on the outer
side of the group of heat exchanger tubes, the necessary data can
be obtained by conducting measurement repeatedly with the positions
of the radiation source and the radiation detector changed
variously.
[0052] The defects of a heat exchanger tube which can be detected
by the apparatus according to the present invention include a
decrease in the wall thickness and a pinhole occurring due to the
corrosion caused by a liquid, cracks in the heat exchanger tube
occurring due to vibration, etc., and other similar defects.
Concretely, a defect of around several 10.sup.-1 mm can be detected
by the apparatus according to the present invention.
[0053] In each of the above-described embodiments, a radiation
source is provided. However, when a group of heat exchanger tubes
are incorporated in a nuclear reactor plant, it is possible to
directly utilize radiations emitted from radioactive nuclides (for
example, sodium-22, sodium-24 and the like) in a coolant as a
radiation source. These radioactive nuclides in the coolant are
produced by nuclear reactions of coolant sodium and neutrons in the
nuclear reactor. Therefore, since it is unnecessary to set a
radiation source additionally, the constitution of the apparatus is
more simplified. This structure can be applied to both a case where
a heat exchanger tube is inspected and a case where a group of heat
exchanger tubes as a whole are inspected collectively.
[0054] As described above, the apparatus according to the present
invention includes a radiation detector inserted in a heat
exchanger tube to be inspected, radiation sources inserted in a
plurality of other heat exchanger tubes surrounding the heat
exchanger tube to be inspected, and a CT processing unit for
subjecting radiation strength signals detected by the radiation
detector to CT processing, whereby a cross section of the heat
exchanger tube to be inspected is imaged by the CT processing. By
such a constitution, the inspection of a heat exchanger tube for
various defects and wall thickness thereof can be carried out
easily, irrespective of the material and structure of the heat
exchanger tube or the condition of arrangement of a multiplicity of
heat exchanger tubes.
[0055] Further, the apparatus according to the present invention
comprises a radiation source set in the interior of a heat
exchanger tube, on the inner side of a group of heat exchanger
tubes, or on the outer side of the group of heat exchanger tubes, a
collimator-carrying radiation detector set on the outer side of the
group of heat exchanger tubes so that the radiations can be
detected on the outer side of the group of heat exchanger tubes and
over substantially the whole of a circumference of the group of
heat exchanger tubes, and a CT processing unit for subjecting
radiation strength signals detected by the radiation detector to
the CT processing, whereby a cross section of the group of heat
exchanger tubes is imaged by the CT processing. By such a
constitution, the inspection of a multiplicity of heat exchanger
tubes as a unit for various defects and wall thickness can be
conducted in practice easily, irrespective of the material and
structure of the heat exchanger tubes or the condition of
arrangement of the multiple heat exchanger tubes.
* * * * *